TY - JOUR T1 - Circumpolar Deep Water Impacts Glacial Meltwater Export and Coastal Biogeochemical Cycling Along the West Antarctic Peninsula JF - Frontiers in Marine Science Y1 - 2019 A1 - Cape, Mattias R. A1 - Vernet, Maria A1 - Pettit, Erin C. A1 - Wellner, Julia A1 - Truffer, Martin A1 - Akie, Garrett A1 - Domack, Eugene A1 - Leventer, Amy A1 - Smith, Craig R. A1 - Huber, Bruce A. KW - Antarctic Peninsula KW - ice KW - meltwater KW - phytoplankton VL - 6 UR - https://www.frontiersin.org/article/10.3389/fmars.2019.00144/full ER - TY - JOUR T1 - The Larsen Ice Shelf System, Antarctica (LARISSA): Polar Systems Bound Together, Changing Fast JF - GSA Today Y1 - 2019 A1 - Wellner, Julia A1 - Scambos, Ted A1 - Domack, Eugene A1 - Vernet, Maria A1 - Leventer, Amy A1 - Balco, Greg A1 - Brachfeld, Stefanie A1 - Cape, Mattias A1 - Huber, Bruce A1 - Ishman, Scott A1 - McCormick, Michael A1 - Mosley-Thompson, Ellen A1 - Pettit, Erin A1 - Smith, Craig A1 - Truffer, Martin A1 - Van Dover, Cindy A1 - Yoo, Kyu-Cheul AB - Climatic, cryospheric, and biologic changes taking place in the northern Antarctic Peninsula provide examples for how ongoing systemic change may pro‐ gress through the entire Antarctic system. A large, interdisciplinary research project focused on the Larsen Ice Shelf system, synthesized here, has documented dramatic ice cover, oceanographic, and ecosystem changes in the Antarctic Peninsula during the Holocene and the present period of rapid regional warming. The responsive- ness of the region results from its position in the climate and ocean system, in which a narrow continental block extends across zonal atmospheric and ocean flow, creating high snow accumulation, strong gradients and gyres, dynamic oceanography, outlet glaciers feeding into many fjords and bays having steep topography, and a continental shelf that contains many glacially carved troughs separated by areas of glacial sedi- ment accumulation. The microcosm of the northern Antarctic Peninsula has a ten- dency to change rapidly—rapid relative not just to Antarctica's mainland but compared to the rest of the planet as well—and it is generally warmer than the rest of Antarctica. Both its Holocene and modern glaciological retreats offer a picture of how larger areas of Antarctica farther south might change under future warming. VL - 29 ER - TY - JOUR T1 - Non-linear glacier response to calving events, Jakobshavn Isbræ, Greenland JF - Journal of Glaciology Y1 - 2019 A1 - Cassotto, Ryan A1 - Fahnestock, Mark A1 - Amundson, Jason M. A1 - Truffer, Martin A1 - Boettcher, Margaret S. A1 - De La Peña, Santiago A1 - Howat, Ian KW - calving KW - dynamic thinning KW - Jakobshavn Isbræ KW - terrestrial radar interferometry KW - tidewater glaciers AB - Jakobshavn Isbræ, a tidewater glacier that produces some of Greenland's largest icebergs and highest speeds, reached record-high flow rates in 2012 (Joughin and others, 2014). We use terrestrial radar interferometric observations from August 2012 to characterize the events that led to record-high flow. We find that the highest speeds occurred in response to a small calving retreat, while several larger calving events produced negligible changes in glacier speed. This non-linear response to calving events suggests the terminus was close to flotation and therefore highly sensitive to terminus position. Our observations indicate that a glacier's response to calving is a consequence of two competing feedbacks: (1) an increase in strain rates that leads to dynamic thinning and faster flow, thereby promoting destabilization, and (2) an increase in flow rates that advects thick ice toward the terminus and promotes restabilization. The competition between these feedbacks depends on temporal and spatial variations in the glacier's proximity to flotation. This study highlights the importance of dynamic thinning and advective processes on tidewater glacier stability, and further suggests the latter may be limiting the current retreat due to the thick ice that occupies Jakobshavn Isbræ's retrograde bed. VL - 65 ER - TY - JOUR T1 - Tracking icebergs with time-lapse photography and sparse optical flow , LeConte Bay , Alaska , 2016 – 2017 JF - J. Glaciol. Y1 - 2019 A1 - Kienholz, Christian A1 - Amundson, Jason M A1 - Motyka, Roman J A1 - Jackson, Rebecca H A1 - Mickett, John B A1 - Sutherland, David A A1 - Nash, Jonathan D A1 - Winters, Dylan S A1 - Dryer, William P A1 - Truffer, Martin KW - glaciological instruments and methods KW - ice KW - icebergs KW - ocean interactions KW - Remote sensing VL - 65 ER - TY - JOUR T1 - Acquisition of a 3 min, two-dimensional glacier velocity field with terrestrial radar interferometry JF - Journal of Glaciology Y1 - 2017 A1 - Voytenko, Denis A1 - Dixon, Timothy H. A1 - Holland, David M. A1 - Cassotto, Ryan A1 - Howat, Ian M. A1 - Fahnestock, Mark A. A1 - Truffer, Martin A1 - De La Peña, Santiago KW - glacier flow KW - glacier geophysics KW - glaciological instruments and methods AB - {\textless}p{\textgreater}Outlet glaciers undergo rapid spatial and temporal changes in flow velocity during calving events. Observing such changes requires both high temporal and high spatial resolution methods, something now possible with terrestrial radar interferometry. While a single such radar provides line-of-sight velocity, two radars define both components of the horizontal flow field. To assess the feasibility of obtaining the two-dimensional (2-D) flow field, we deployed two terrestrial radar interferometers at Jakobshavn Isbrae, a major outlet glacier on Greenland's west coast, in the summer of 2012. Here, we develop and demonstrate a method to combine the line-of-sight velocity data from two synchronized radars to produce a 2-D velocity field from a single (3 min) interferogram. Results are compared with the more traditional feature-tracking data obtained from the same radar, averaged over a longer period. We demonstrate the potential and limitations of this new dual-radar approach for obtaining high spatial and temporal resolution 2-D velocity fields at outlet glaciers.{\textless}/p{\textgreater} UR - https://www.cambridge.org/core/product/identifier/S0022143017000284/type/journal{\_}article ER - TY - JOUR T1 - Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier JF - Nature Y1 - 2017 A1 - Smith, J. A. A1 - Andersen, T. J. A1 - Shortt, M. A1 - Gaffney, A. M. A1 - Truffer, Martin A1 - Stanton, T P A1 - Bindschadler, Robert A1 - Dutrieux, Pierre A1 - Jenkins, Adrian A1 - Hillenbrand, C.-D. A1 - Ehrmann, Werner A1 - Corr, H. F. J. A1 - Farley, N. A1 - Crowhurst, S. A1 - Vaughan, David G. KW - Antarctica KW - Pine Island glacier AB - The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreat is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Thus our results suggest that, even when climate forcing weakened, ice-sheet retreat continued. VL - 541 UR - http://dx.doi.org/10.1038/nature20136{%}5Cnhttp://www.nature.com/doifinder/10.1038/nature20136 http://www.nature.com/articles/nature20136 ER - TY - JOUR T1 - Sensitivity of Pine Island Glacier to observed ocean forcing JF - Geophysical Research Letters Y1 - 2016 A1 - Christianson, Knut A1 - Bushuk, Mitchell A1 - Dutrieux, Pierre A1 - Parizek, Byron R. A1 - Joughin, Ian R. A1 - Alley, Richard B. A1 - Shean, David E. A1 - Abrahamsen, E. Povl A1 - Anandakrishnan, Sridhar A1 - Heywood, Karen J. A1 - Kim, Tae-Wan A1 - Lee, Sang Hoon A1 - Nicholls, Keith A1 - Stanton, Tim A1 - Truffer, Martin A1 - Webber, Benjamin G. M. A1 - Jenkins, Adrian A1 - Jacobs, Stan A1 - Bindschadler, Robert A1 - Holland, David M. KW - glacier-ocean interactions KW - Ice Dynamics KW - ice shelves KW - ice streams KW - marine ice sheet instability AB - ©2016. American Geophysical Union. All Rights Reserved.We present subannual observations (2009–2014) of a major West Antarctic glacier (Pine Island Glacier) and the neighboring ocean. Ongoing glacier retreat and accelerated ice flow were likely triggered a few decades ago by increased ocean-induced thinning, which may have initiated marine ice sheet instability. Following a subsequent 60{%} drop in ocean heat content from early 2012 to late 2013, ice flow slowed, but by {\textless} 4{%}, with flow recovering as the ocean warmed to prior temperatures. During this cold-ocean period, the evolving glacier-bed/ice shelf system was also in a geometry favorable to stabilization. However, despite a minor, temporary decrease in ice discharge, the basin-wide thinning signal did not change. Thus, as predicted by theory, once marine ice sheet instability is underway, a single transient high-amplitude ocean cooling has only a relatively minor effect on ice flow. The long-term effects of ocean temperature variability on ice flow, however, are not yet known. VL - 43 UR - http://doi.wiley.com/10.1002/2016GL070500 ER - TY - JOUR T1 - Dynamic jamming of iceberg-choked fjords JF - Geophys. Res. Lett. Y1 - 2015 A1 - Peters, I A1 - Amundson, J. M. A1 - Cassotto, R A1 - Fahnestock, M A1 - Darnell, K A1 - Truffer, M. A1 - Zhang, W. KW - 10.1002/2014GL062715 and glaciers KW - calving KW - icebergs KW - jamming VL - 42 ER - TY - JOUR T1 - 21st-century increase in glacier mass loss in the Wrangell Mountains, Alaska, USA, from airborne laser altimetry and satellite stereo imagery JF - J. Glaciol. Y1 - 2014 A1 - Das, Indrani A1 - Hock, Regine A1 - Berthier, Etienne A1 - Lingle, Craig S. KW - glacier mass balance KW - ice and climate VL - 60 UR - http://www.igsoc.org/journal/60/220/j13J119.html ER - TY - JOUR T1 - Boundary condition of grounding lines prior to collapse, Larsen-B Ice Shelf, Antarctica JF - Science Y1 - 2014 A1 - Rebesco, M A1 - Domack, E A1 - Zgur, F A1 - Lavoie, C A1 - Leventer, A A1 - Brachfeld, S A1 - Willmott, V A1 - Halverson, G A1 - Truffer, M A1 - Scambos, T A1 - Pettit, Erin C PB - American Association for the Advancement of Science VL - 345 ER - TY - JOUR T1 - Estimating glacier snow accumulation from backward calculation of melt and snowline tracking JF - Annals of Glaciology Y1 - 2013 A1 - Hulth, J. A1 - DENBY, C.R. A1 - Regine Hock VL - 54 ER - TY - JOUR T1 - The evolution of crystal fabric in ice sheets and its link to climate history JF - Journal of Glaciology Y1 - 2013 A1 - Joseph H Kennedy A1 - Erin C Pettit A1 - Di Prinzio, Carlos L AB - The evolution of preferred crystal-orientation fabrics is strongly sensitive to the initial fabric and texture. A perturbation in climate can induce variations in fabric and texture in the firn. Feedbacks between fabric evolution and ice deformation can enhance these variations through time and depth in an ice sheet. We model the evolution of fabric under vertical uniaxial compression and pure shear regimes typical of ice divides. Using an analytic anisotropic flow law applied to an aggregate of distinct ice crystals, the model evolves the fabric and includes parameterizations of crystal growth, polygonization and migration recrystallization. Stress and temperature history drive the fabric evolution. Using this model, we explore the evolution of a subtle variation in near-surface fabric using both constant applied stress and a stress-temperature history based on data from Taylor Dome, East Antarctica. Our model suggests that a subtle variation in fabric caused by climate perturbations will be preserved through time and depth in an ice sheet. The stress history and polygonization rate primarily control the magnitude of the preserved climate signal. These results offer the possibility of extracting information about past climate directly from ice fabrics. VL - 59 UR - http://glacierstest.gi.alaska.edu/sites/default/files/bibfiles/t12J159.pdf IS - 214 ER - TY - JOUR T1 - Rapid Submarine Melting Driven by Subglacial Discharge, LeConte Glacier, Alaska JF - Geophysical Research Letters Y1 - 2013 A1 - Roman J. Motyka A1 - Dryer, W. P. A1 - Jason M Amundson A1 - Martin Truffer A1 - Mark Fahnestock KW - frontal ablation KW - submarine melting KW - tidewater glaciers AB - We show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers. This buoyant discharge draws in warm seawater, entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice. To capture the effects of subglacial discharge on submarine melting, we conducted 4 days of hydrographic transects during late summer 2012 at LeConte Glacier, Alaska. A major rainstorm allowed us to document the influence of large changes in subglacial discharge. We found strong submarine melt fluxes that increased from 9.1 ± 1.0 to 16.8 ± 1.3 m d−1 (ice face equivalent frontal ablation) as a result of the rainstorm. With projected continued global warming and increased glacial runoff, our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems. These effects must be considered when modeling glacier response to future warming and increased runoff. VL - 40 UR - http://dx.doi.org/10.1002/grl.51011 ER - TY - JOUR T1 - Recent air and ground temperature increases at Tarfala Research Station, Sweden JF - Polar Research Y1 - 2013 A1 - Ulf Jonsell A1 - Regine Hock A1 - Martial Duguay KW - Air temperature KW - climate change KW - degree-days KW - lapse rate KW - NAO KW - permafrost AB - Long-term data records are essential to detect and understand environmental change, in particular in generally data-sparse high-latitude and high-altitude regions. Here, we analyse a 47-year air temperature record (1965-2011) at Tarfala Research Station (67° 54.7'N, 18° 36.7'E, 1135 m a.s.l.) in northern Sweden, and a nearby 11-year record of 100-m-deep ground temperature (2001-11; 1540 m a.s.l.). The air temperature record shows a mean annual air temperature of -3.5±0.9°C (±1 standard deviation s) and a linear warming trend of ±0.042°C yr-1. The warming trend shows large month-to-month variations with the largest trend in January followed by October. Also, the number of days with positive mean daily temperatures and positive degree-day sums has increased during the last two decades compared to the previous period. Temperature lapse rates derived from the mean daily Tarfala record and an air temperature record at the borehole site average 4.5°C km-1 and tend to be higher in summer than in winter. Mean summer air temperatures at Tarfala explain 76% of the variance of the summer glacier mass balance of nearby Storglacia¨ren. Consistent with the observed increase in Tarfala’s air temperature, the ground temperature record shows significant permafrost warming with the largest trend (0.047°C yr-1) found at 20 m depth.Keywords: Air temperature; climate change; permafrost; lapse rate; degree-days; NAO(Published: 15 July 2013)Citation: Polar Research 2013, 32, 19807, http://dx.doi.org/10.3402/polar.v32i0.19807 VL - 32 UR - http://www.polarresearch.net/index.php/polar/article/view/19807 ER - TY - JOUR T1 - From ice-shelf tributary to tidewater glacier: continued rapid recession, acceleration and thinning of Rohss Glacier following the 1995 collapse of the Prince Gustav Ice Shelf, Antarctic Peninsula JF - Journal of Glaciology Y1 - 2011 A1 - Glasser, NF A1 - Scambos, TA A1 - Bohlander, J. A1 - Martin Truffer A1 - Erin C Pettit A1 - Davies, BJ VL - 57 UR - http://openurl.ingenta.com/content/xref?genre=article&issn=0022-1430&volume=57&issue=203&spage=397 ER - TY - JOUR T1 - Mountain glaciers and ice caps around Antarctica make a large sea-level rise contribution JF - Geophysical Research Letters Y1 - 2009 A1 - Regine Hock A1 - de Woul, M. A1 - Valentina Radić A1 - Dyurgerov, M. VL - 36 ER - TY - JOUR T1 - Benchmark experiments for higher-order and full Stokes ice sheet models (ISMIP-HOM) JF - The Cryosphere Y1 - 2008 A1 - Frank Pattyn A1 - Perichon, L. A1 - Andy Aschwanden A1 - Breuer, B. A1 - de Smedt, B. A1 - Gagliardini, O. A1 - Gudmundsson, G. H. A1 - Hindmarsh, R. C. A. A1 - Hubbard, A. L. A1 - Jesse V Johnson A1 - Kleiner, T. A1 - Konovalov, Y. A1 - Martin, C. A1 - Payne, A. J. A1 - David Pollard A1 - Stephen F. Price A1 - M Rückamp A1 - Fuyuki Saito A1 - Souček, O. A1 - Sugiyama, S. A1 - Zwinger, T. VL - 2 ER - TY - JOUR T1 - Candidate drill site near the Ross-Amundsen ice divide, West Antarctica JF - DRAFT, Mar Y1 - 2005 A1 - Conway, H A1 - Neumann, TA A1 - Stephen F. Price A1 - Waddington, ED A1 - Morse, D A1 - Taylor, K A1 - Mayewski, PA A1 - Dixon, D A1 - Erin C Pettit A1 - Steig, EJ ER - TY - JOUR T1 - Proposed drill site near the Ross–Amundsen ice divide, West Antarctica JF - White Paper for the US Ice Core Working Group Y1 - 2005 A1 - Conway, H A1 - Neumann, TA A1 - Stephen F. Price A1 - Waddington, ED A1 - Morse, D A1 - Taylor, K A1 - Mayewski, PA A1 - Dixon, D A1 - Erin C Pettit A1 - Steig, EJ ER -